1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a sealant pattern of an LCD device manufactured by applying a liquid crystal to the surface of a substrate.
2. Discussion of the Related Art
Generally, ultra thin flat panel displays have a display screen with a thickness of several centimeters or less. In particular, flat panel LCD devices are widely used in monitors for notebook computers, spacecraft, and aircraft because such LCD devices have low power consumption and are easy to carry.
Such an LCD device includes a lower substrate, an upper substrate, and a liquid crystal layer. A thin film transistor (TFT) and a pixel electrode are formed on the lower substrate. The upper substrate is formed to oppose the lower substrate. A light-shielding layer, a color filter layer, and a common electrode are formed on the upper substrate. The liquid crystal layer is formed between the lower and upper substrates. In operation an electric field is formed between the lower and upper substrates by the pixel electrode and the common electrode so that the electric field “drives” the alignment of molecules in the liquid crystal layer. Light transmittivity is controlled by driving the liquid crystal layer so that a picture image is displayed.
In the aforementioned LCD device, to form the liquid crystal layer between lower and upper substrates, a vacuum injection method based on capillary phenomenon and pressure difference has been conventionally used. However, such a vacuum injection method has a problem in that it takes long time to inject the liquid crystal into a large display panel, thereby reducing manufacturing productivity.
To solve such a problem, a method of applying liquid crystal on the substrate has been developed and is generally described with reference to FIGS. 1A to 1D. Although the drawings illustrate only one unit cell, a plurality of unit cells may be formed depending upon the size of the substrate.
As shown in FIG. 1A, a lower substrate 1 and an upper substrate 3 are prepared. A plurality of gate and data lines (not shown) are formed on the lower substrate 1. The gate lines cross the data lines to define a pixel region. A thin film transistor (not shown) is formed at each crossing point between the gate and data lines. A pixel electrode (not shown) connected with the thin film transistor is formed in the pixel region.
A light-shielding layer (not shown) is formed on the upper substrate 3 to prevent light from leaking out from the gate and data lines and the thin film transistor. Color filter layers of red(R), green(G), and blue(B) are formed on the light-shielding layer, and a common electrode is formed on the color filter layers. An alignment film (not shown) is formed on at least one of the lower substrate 1 and the upper substrate 3 to initially align the liquid crystal molecules.
As shown in FIG. 1B, a sealant 7 is formed on the lower substrate 1 and a liquid crystal 5 is applied thereon, so that a liquid crystal layer is formed. A spacer (not shown) is spread or sprayed onto the upper substrate 3 to maintain a cell gap between the upper and lower substrates.
In the method of manufacturing the LCD device based on the liquid crystal application method, a liquid crystal layer is formed on attached substrates before the sealant 7 is hardened. Therefore, if a thermo-hardening sealant is used as the sealant 7, the liquid crystal heats and expands so that it flows out of the substrate when it is heated. For this reason, a problem arises in that the liquid crystal 5 is contaminated. Therefore, in the method of manufacturing the LCD based on the liquid crystal application method, a sealant that is at least partially curable by ultraviolet (UV) light is used as the sealant 7.
The UV sealant is formed by a screen printing method or a dispensing method. In the screen printing method, since a screen comes into contact with the substrate, the alignment film formed on the substrate may be damaged. Also, if the substrate has a large sized area, loss of the sealant increases. In these respects, the dispensing method is preferably used.
As shown in FIG. 1C, the lower substrate 1 is attached to the upper substrate 3.
As shown in FIG. 1D, UV light is irradiated through a UV irradiating device 9 so that the sealant 7 is hardened.
Thereafter, although not shown, a cell cutting process and a final test process are performed, thereby completing a liquid crystal cell.
Meanwhile, FIGS. 2A and 2B are perspective views illustrating a process of forming a UV sealant using a dispensing method. In the method of applying liquid crystal to one of the substrates before attaching the the substrates, since no liquid crystal injection hole is required, a sealant 7 having no injection hole is formed on a lower substrate 1 using a dispensing device 8.
However, since the sealant 7 has high viscosity, it is concentrated upon the end of a nozzle of the dispensing device 8 before the sealant 7 is dispensed. For this reason, a blob “A” of the sealant 7 is excessively deposited at the point where deposition of the sealant 7 on the substrate is started.
As shown in FIG. 2C, the excessively distributed sealant spreads into an active region (central part of the substrate) and a dummy region (outer part of the substrate) when the lower substrate 1 is attached to the upper substrate 3. In this case, a problem arises in that the sealant spreads into the active region and contaminates the liquid crystal while the sealant spread out to the dummy region makes the cell cutting process difficult, especially after the sealant is cured.